1. Field
The present application relates to a multilayer film reflector, a method of manufacturing a multilayer film reflector, a projection optical system, an exposure apparatus, and a method of manufacturing a device.
2. Description of the Related Art
For example, an EUV exposure apparatus disclosed in Patent Document 1: U.S. Patent Application Publication No. 2005/157384 has been suggested as an exposure apparatus used in a photolithography process. A multilayer film reflector capable of reflecting extreme ultra-violet (EUV) light has been used in a projection optical system of the EUV exposure apparatus.
A uniform period multilayer film which is the most general multilayer film has a simple configuration in which two layers (a layer pair) having different refractive indices are laminated with a uniform period. In order to increase NA of the projection optical system, it is necessary to reflect EUV light having a wide angle range. Meanwhile, in the uniform period multilayer film having the simple configuration, it is difficult to increase a reflection angle range of the EUV light.
In contrast, in a non-uniform period multilayer film, since film thicknesses of all layers are arbitrarily determined, it is possible to obtain a substantially constant reflectivity in a wide angle range. However, in the non-uniform period multilayer film, since the number of adjustment parameters at the time of film deposition is also increased as the number of design parameters is increased, time and labor are required until reflection characteristics as designed are achieved.
In view of such circumstances, it is a proposition to provide a high-functional multilayer film reflector with a simple configuration, a method of manufacturing the multilayer film reflector, a projection optical system using the multilayer film reflector, an exposure apparatus using the projection optical system, and a method of manufacturing a high-functional device.